Mideast: Two bombings, for which Hamas claims responsibility, halt attempts to revive peace talks. Israeli officials order closure of West Bank and Gaza Strip.

JERUSALEM — In brutally synchronized attacks, two suicide bombers in dark business suits blew themselves up in a crowded Jerusalem market Wednesday, killing 13 other people and wounding nearly 170.

The bombings, the first in more than four months and the deadliest in more than a year, brought an immediate halt to efforts to revive the moribund Israeli-Palestinian peace process. U.S. special envoy Dennis B. Ross canceled a visit to the region that was to begin today, and Israeli leaders called off low-level talks announced earlier in the week.

Israel ordered Palestinian workers to return home and slapped a closure on the West Bank and Gaza Strip, preventing Palestinians from moving between their own cities and villages. The government also ordered its security forces to crack down on Palestinian extremists and threatened, according to Israel Radio, to reenter Palestinian areas to make arrests if the Palestinian Authority's efforts are not considered sufficient.

The militant Islamic group Hamas claimed responsibility for the attacks in a leaflet discovered late Wednesday in the Palestinian-controlled city of Ramallah, about 15 miles north of Jerusalem. The leaflet, signed by the movement's military wing, gave Israel until 9 p.m. Sunday to release all Palestinian prisoners but did not specify actions it would take if the demand was not met.

The bombs, which police said were laced with nails and metal shards to maximize damage, tore through the maze-like streets of the popular Mahane Yehuda market at midday, when its alleyways were jammed with lunch-hour shoppers and visitors.

Dazed store owners and other witnesses later said they saw two men wearing suits, white shirts and ties and carrying large attache cases just before the explosions left scenes of horror about 50 yards apart. The dead and wounded lay among the market's mangled stalls, blood mingling in puddles with water and crushed melons.

"I saw the dead, old men, a woman, blood everywhere," said Benny Cohen, 45, the owner of a vegetable stand around the corner from the first explosion, which occurred outside a shoe store. "Where is the peace?"

As he spoke, Israeli soldiers and police rounded up scores of young Palestinian men who work in the market. Several were seen with bloodied noses and other possible signs of spontaneous retaliation.

Palestinian Authority President Yasser Arafat publicly condemned the bombings as the actions of terrorists who harm the peace process, and telephoned Prime Minister Benjamin Netanyahu to offer condolences.

"I condemn completely these terrorist activities because it is against the peace process, against the Palestinians and against the Israelis," Arafat said at a news conference in the West Bank city of Jericho. "We'll do all [in] our capability to face these terrorist activities and terrorist groups. . . . We are doing all our best."

Netanyahu reacted harshly, accusing the Palestinian leader of failing to crack down on extremists and angrily demanding that the Palestinian Authority wage a "war against terror."

"Words of condolence are not enough," Netanyahu told reporters after visiting some of the wounded at a Jerusalem hospital. "We have the right to demand of those who call themselves our partners in peace to be partners in peace."

He said those who carry out attacks like the Jerusalem bombings "get guidance, get support, they get incentive from inside the territories of the Palestinian Authority."

President Clinton in Washington also denounced the bombings as a "barbarous act" and pressed Arafat to take action against extremists. He urged the Palestinians to increase their security cooperation with Israel, suspended since March.

The peace negotiations collapsed in March following Netanyahu's decision to begin construction of a Jewish housing development on the outskirts of traditionally Arab East Jerusalem. In response to the groundbreaking, a Hamas suicide bomber blew up a trendy Tel Aviv cafe March 21, killing three other people and injuring scores.

In Wednesday's bombing, there was an early report that a different extremist group, Islamic Jihad, had claimed responsibility, but the government took the Hamas claim seriously.

President Ezer Weizman said he believed that the market attack may have been in response to the city's announcement last week that it had approved construction of another Jewish housing project in the Palestinian neighborhood of Ras al Amud in East Jerusalem. Netanyahu's government has said it will not allow that project to go forward for now, but Palestinians are angry.

Asked if these developments may have prompted the attacks, Weizman said, "The truth? I believe so." He added that another recent incident, the distribution by an Israeli of a poster depicting the prophet Muhammad as a pig, also may have helped create the atmosphere that led to the bombings.